JP2003343236A - Low frequency sound damping method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of a low frequency noise which is a 'hum ming' phenomenon of an internal combustion engine. <P>SOLUTION: In a low frequency sound damping method, the low frequency sound is suppressed from occurring by making the sound pressure propagation distance between each cylinder and silencer of a plurality of cylinders of an internal combustion engine in an exhaust gas passage of the internal combustion engine 1 uniform to reduce the sound, and a phase adjusting part 3 is provided at upstream side of the silencer 4. In a low frequency sound damping device, the silencer 4 is provided with a clearance 11 between a noise absorbing material 10 and a silencing part casing 9 provided in an exhaust gas passage. The phase adjusting part is comprised of an adjusting pipe group different in length for making the sound pressure propagation distance of a plurality of each cylinder in the internal combustion engine uniform, and a shutter for selecting either of the adjusting pipe group. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a low frequency attenuation type silencing method and device for attenuating low frequency noise of an internal combustion engine.

[0002]

2. Description of the Related Art A conventional method for attenuating noise from an internal combustion engine is to expand a part of an exhaust pipe to reduce sound by expanding an exhaust passage, or to branch a passage of an exhaust pipe to form a resonance chamber. A common method is to provide noise attenuation due to resonance,
In recent years, sound absorbing materials such as glass fibers, carbon fibers, and metal fibers have been used together or alone. A method for reducing attenuation due to resonance is disclosed in Japanese Utility Model Laid-Open No. 1-174562.
As in 7-293377, a cylinder-shaped container is used as a resonance chamber, and a piston-shaped lid is moved back and forth to change the volume inside the container.
In some cases, the noise frequency to be silenced is adjusted so that it resonates. Furthermore, as seen in JP-A-8-137478 and the like,
There is also an example in which a sensor microphone that detects a noise wave propagating from a noise source and transmits a signal related to the noise wave to an active muffling speaker mechanism via a controller is arranged at the entrance side of the sound tuner.

The basic frequency of a multi-cylinder diesel engine is 20 to
At 100Hz, the wavelength of sound is as long as 5 to 30m, and it is necessary to install a silencer of excessive size for low frequency attenuation. Further, the noise from the marine internal combustion engine (diesel engine) is as shown in the graph of FIG. 6 (when the solid line is the source sound and the chain double-dashed line is a silencer) Since the exhaust gas piping distance is different, even if it is possible to reduce the noise by 10 to 30 dB in the middle and high sound frequencies, it is almost impossible to reduce it in the low frequencies.
It is considered that the change in the pressure (sound pressure) P due to the exhaust gas at regular intervals at the source is as shown in FIG.
During the propagation to the silencer, the cylinders have unequal intervals as shown in FIG. 8, and low-frequency noise is generated as a "beat" phenomenon.

[0004]

Therefore, even when the exhaust gas pipe distance from each cylinder of the internal combustion engine to the silencer is different, the inventors of the present invention use periodic exhaust for each cylinder while propagating to the silencer. The pressure (sound pressure) changes were studied so that they would not become unequal intervals, and it was considered to suppress the generation of low-frequency noise, which is a "beat" phenomenon. As a matter of course, by installing a muffling section, it is possible to muffle the sound in the middle and high frequencies.

[0005]

As a result of studying the above-mentioned problems, as a result of equalizing the sound pressure propagation distance between each of the plurality of cylinders of the internal combustion engine and the silencer in the exhaust gas flow path of the internal combustion engine, A low-frequency attenuation type silencing method is characterized in that the silencing is performed after suppressing the generation of frequency sound. In order to implement this low frequency attenuation type silencing method, a low frequency attenuation type silencing device is provided which is provided with a phase adjusting unit upstream of the silencing unit provided in the exhaust gas flow path of the internal combustion engine. Of.

Further, in the sound deadening part of this low frequency attenuation type sound deadening device, a gap is provided between the sound absorbing material provided in the exhaust gas passage and the sound deadening part casing. The sound absorption coefficient of the sound absorbing material drops sharply in the low frequency range. Therefore, an air layer is provided between the sound absorbing material and the muffling section casing to increase the sound reducing effect and the heat insulating effect. In addition, the thickness of the sound absorbing material can be increased.

The phase adjusting section in the low-frequency attenuation type silencer of the present invention has unequal intervals for each cylinder while the pressure (sound pressure) changes accompanying the periodic exhaust gas are propagated to the silencer at equal intervals. Is also a means for performing adjustment to restore the original periodic exhaust gas at regular intervals. There are various possible mechanisms for the phase adjusting unit. For example, although there is a problem in practicality, an exhaust gas pipe system is installed so that each cylinder has the same length. The most preferable structure is a structure including adjustment tube groups having different lengths for equalizing sound pressure propagation distances of a plurality of cylinders of the internal combustion engine, and a shutter for selecting one of the adjustment tube groups.
The shutter has a rotation selection board with a vent hole in a part of the disc,
It is preferable that it comprises a synchronous motor for driving the rotation selection board. The adjusting tube may be provided with a sound absorbing means such as a resonance chamber and an expansion chamber in the hollow tube.

[0008]

1 is a side view of an example in which a low frequency attenuation type silencer of the present invention is provided in a diesel engine. Figure 2
3 is a cross-sectional view of the phase adjusting unit, and FIG. 3 is a cross-sectional view taken along the line AA in FIG. The internal combustion engine 1 shown in this example has cylinders C1 and C
It is a 6-cylinder diesel engine with 2, C3, C4, C5, and C6.
A phase adjusting unit 3 and a muffling unit 4 are provided on the downstream side of the exhaust pipe line 2 serving as an exhaust gas flow path. The phase adjusting unit 3 is on the upstream side of the muffling unit 4. The sound pressure propagation distance before reaching the phase adjusting unit 3 of the cylinder C1 is the longest, and the sound pressure propagation distance is sequentially shortened to C2, C3, C4, C5, C6.

FIG. 2 shows an example of the structure of the phase adjusting section 3. The tubular casing 3a has an exhaust gas inlet 5 and an exhaust gas outlet 6 which communicate with the exhaust gas passage of the exhaust pipe line 2. Exhaust gas from the exhaust gas outlet 6 flows to the muffling section 4. A rotation selection board 7 is installed inside the cylindrical casing 3a so as to be rotated by a synchronous motor 8. Rotation selection board 7
A ventilation hole 7a is provided in the. Synchronous motor 8 is cylinder C
The rotation selection board 7 is rotated in synchronization with the driving of 1, C2, C3, C4, C5, C6.

Similarly, phase adjusting tubes D1, D2, D3, D4, D5, D6 having different sound pressure propagation distances are arranged inside the cylindrical casing 3a on concentric circles. When the rotation selection board 7 is rotated, the ventilation hole 7a is aligned with one of the phase adjusting pipes D so that the exhaust gas inlet 5, the phase adjusting pipe D and the exhaust gas outlet 6 can be communicated with each other. The phase adjusting tube D is a hollow tube in this example, but if necessary for sound deadening performance, a means having a sound deadening effect such as a resonance chamber or an expansion chamber may be provided inside the hollow tube. The phase adjustment tube is formed shorter in the order of D1-D2-D3-D4-D5-D6. The order of arrangement on the concentric circles is the firing order of D1-D5-D3-D6-D2-D4 in the rotational direction so as to correspond to the sound pressure propagation distances of different lengths. In the case of the maximum sound pressure propagation distance difference (maximum phase difference distance) L, the length of the longest phase adjustment tube D1 is appropriately L / 2 to L.

In the case of a diesel engine, the ignition sequence is, for example, ignition in the order of cylinders C1-C5-C3-C6-C2-C4 to provide a smooth drive source. As a result, the pressure (sound pressure) change accompanying the above-described conventional periodic cylinder-by-cylinder exhaust becomes unequal intervals (Fig. 8) during propagation, resulting in a "beat" phenomenon. However, this is solved by providing the phase adjusting unit 3 on the upstream side of the muffling unit 4 in the exhaust gas flow path as in the present invention. That is, in order to correspond to the change in the sound pressure propagation distance of C1-C5-C3-C6-C2-C4 in the cylinder ignition sequence, the arrangement order on the concentric circle is D1-D5-D3-D6-
The ventilation hole 7a of the rotation selection board 7 which is the shutter at the base of the phase adjustment tube D2-D4 is synchronously rotated by the synchronous motor 8,
The sound pressure propagation distance reaching the muffling section 4 is adjusted (the sound pressure propagation distance is made uniform) by sequentially selecting the phase adjustment tubes D1-D5-D3-D6-D2-D4, and the sound pressure changes periodically at equal intervals. (See FIG. 7).

FIG. 4 is a sectional view of the muffling section 4. Silencer 4
Is disposed on the downstream side of the phase adjusting unit 3, and the phase adjusting unit 3 silences the exhaust gas whose phase is adjusted to change the sound pressure at regular intervals. Silencer 4
The structure of is such that there is a gap between the sound deadening casing 9 and the sound absorbing material 10.
It is a structure with 11 (50 to 300 mm). The sound absorbing material 10 is provided so as to absorb the exhaust gas flow path from the outer periphery.
The sound absorption coefficient of is drastically reduced in the low frequency range. Therefore, a gap 11 is provided between the sound absorbing material 10 and the muffling section casing 9 and an air layer is provided to increase the muffling effect in the low frequency range.

This is shown in FIG. 10 in the medium and high sound range
In addition to being able to reduce the noise by ~ 30dB, it is possible to reduce the noise by 20dB even in the low frequency range.

[0014]

EFFECT OF THE INVENTION The low-frequency attenuation type silencer method and apparatus according to the present invention has a structure in which the exhaust gas pipe distance from each cylinder of a plurality of internal combustion engines to the silencer is different, and the pressure (sound generated by periodic exhaust of each cylinder Even if the pressure changes become uneven,
During propagation to the silencer, the phase adjuster adjusts the phase to a periodic change in sound pressure at equal intervals, so that it is possible to suppress the occurrence of low-frequency noise, which is a “beat” phenomenon.

Moreover, in addition to the silencing of the middle and high sound waves in the silencing part, the gap portion is provided, so that silencing of the bass part is also possible. These eliminate the previously difficult deployment of oversized silencers, which was previously required for low frequency attenuation, especially on ships.

[Brief description of drawings]

FIG. 1 is a side view of an example in which a low frequency attenuation type silencer of the present invention is provided in a diesel engine.

FIG. 2 is a sectional view of a phase adjusting unit.

FIG. 3 is a sectional view taken along line AA in FIG.

FIG. 4 is a sectional view of a muffling section.

FIG. 5 is a graph of sound pressure measurement results for each frequency when the source sound and the silencer of the present invention are provided.

FIG. 6 is a graph of sound pressure for each frequency when a source sound and a conventional silencer are provided.

FIG. 7: Pressures associated with periodic exhaust of the source at regular intervals
It is a graph which shows (sound pressure) change.

FIG. 8: Unequally spaced pressure during propagation to the silencer
It is a graph which shows (sound pressure) change.

[Explanation of symbols]

1 Internal combustion (diesel) engine 2 exhaust pipe 3 Phase adjuster 4 silencer 5 Exhaust gas inlet 6 exhaust gas outlet 7 rotation selection board 8 synchronous motor 9 Muffler casing 10 sound absorbing material 11 Gap C1, C2, C3, C4, C5, C6 Cylinder D6, D5, D4, D3, D2, D1 Phase adjustment tube

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takeo Aya             1421-2 Midorigaoka, Ikoma City, Nara Prefecture (72) Inventor Koujiro Yoshida             2-2-14 Tsuda Motomachi, Hirakata City, Osaka Prefecture (72) Inventor Kenji Yamane             2-2-17 Tsudamotomachi, Hirakata City, Osaka Prefecture F-term (reference) 3G004 AA05 BA01 CA01 CA13 DA01                       DA06 DA11 DA21 EA01                 5D061 EE40

Claims (5)

[Claims] 1. A silencer while suppressing the generation of low-frequency noise by equalizing the sound pressure propagation distance between each silencer and a plurality of cylinders of the internal combustion engine in the exhaust gas flow path of the internal combustion engine. A low-frequency attenuation type silencing method characterized by: 2. A low-frequency attenuation type silencer comprising a phase adjuster provided upstream of a silencer provided in an exhaust gas passage of an internal combustion engine. 3. The low frequency attenuation type silencer according to claim 2, wherein a gap is provided between the sound absorbing material provided in the exhaust gas flow passage and the silencer casing. 4. A group of adjusting tubes having different lengths for equalizing the sound pressure propagation distance of each of the plurality of cylinders of the internal combustion engine by the phase adjusting unit,
The low-frequency attenuation type silencer according to claim 2, further comprising a shutter that selects any one of the adjustment tube groups. 5. The low frequency attenuation type silencer according to claim 4, wherein the shutter comprises a rotary selection board having a vent hole in a part of the disk and a synchronous motor for driving the rotation selection board.